Process and installation for controlling the quantity of solid particles emitted by a combustion turbine

ABSTRACT

The invention concerns a method of controlling the quantity of solid particles emitted by a combustion turbine ( 1 ), during the combustion of a liquid fuel, by injecting a combustion catalyst suitable for reducing the quantity of solid particles generated during combustion. 
     This method comprises the following steps:
         Measuring the quantity of particles (Qsuies) emitted during combustion;   Injecting the combustion catalyst into the combustion turbine ( 1 ) when the quantity of particles measured is higher than a maximum threshold value; and   Stopping the injection of the catalyst when the measured quantity of particles is lower than a minimum target value.

The present invention concerns combustion turbines or gas turbines, andconcerns specifically the controlling of concentration of solidparticles emitted by gas turbines during the combustion of a liquidfuel.

A wide range of liquid fuels available for feeding the combustionturbines. This mainly includes heavy fuel oils, crude oils, heavy orlight distilled oils, gas oils, kerosene, naphtha, biodiesel,bioethanol, etc.

A heavy oil type fuel contains vanadium and other types of contaminants,including sulfur, and consequently, its combustion generates solid ashsimilar to solid particles.

Based on the performance of the combustion system in the constitution ofa combustion turbine, the liquid or gaseous fuels may generate emissionsof dust or ash, and generally, solid particles, which are released tothe atmosphere, through a chimney.

Among the solid particles, soot corresponds to the organic fraction ofdust, and includes carbon, hydrogen and possibly, oxygen and nitrogen,to a major extent.

The solid particles may also contain a mineral fraction, generallyconsisting of alkali metals or heavy metals.

The regulations related to combustion turbines imposed globally orlocally across the countries set maximum limits for emission of solidparticles into the atmosphere.

For example, when a combustion turbine using a liquid fuel is working atits rated speed, the maximum value of emission of dust from a stationarycombustion turbine to the atmosphere should be 50 mg/Nm³.

In order to restrict the quantity of solid particles emitted, acombustion catalyst is generally used.

There are different types of combustion catalysts that are capable ofreducing soot emissions in installations. The choice of the combustioncatalyst depends on the type of fuel, the type installation used and themaximum concentration of solid particles imposed by the regulations.

In the light of the foregoing, the present invention has the objectiveof controlling the quantity of solid particles emitted by a combustionturbine, regardless of the operating regimes of the combustion turbine.

Thus, the invention has the primary objective of providing a method ofcontrolling the quantity of solid particles emitted by a combustionturbine, during the combustion of a liquid fuel, by injecting acombustion catalyst suitable for reducing the quantity of solidparticles generated during combustion.

This method comprises the following steps:

Measuring the quantity of particles emitted during combustion;

Injecting the combustion catalyst into the combustion turbine when thequantity of particles measured is higher than a maximum threshold value;

Stopping the injection of the catalyst when the measured quantity ofparticles is lower than a minimum threshold value.

These process steps allow to implement the cyclic phases, keeping inview the hysteresis of injection of catalyst, thus enabling a moreprecise control of the quantity of emitted particles and/or optimizingthe consumption of combustion catalyst.

Advantageously, the temperature of the flame of the combustion turbineis more than or equal to 1363 K (1090° C.).

For example, the catalyst is injected into a liquid fuel system feedline upstream of the combustion system of the combustion turbine.

Alternatively, the catalyst can be injected directly into the combustionturbine unit.

Advantageously, the maximum threshold value of concentration ofparticles is between 45 mg/Nm³ and 55 mg/Nm³. This range ofconcentration relates to the maximum limit value of emission ofparticles to the atmosphere imposed by the regulatory authoritiesworldwide.

With respect to the minimum target value, this concentration ofparticles is between 20 mg/Nm³ and 30 mg/Nm³.

Preferably, the combustion catalyst includes at least an elementselected from iron (III) oxides, cerium (III) oxides, cerium (IV) oxidesand their mixtures.

Preferably, the quantity of particles emitted is measured continuously.

The invention also has the objective of controlling the quantity ofsolid particles emitted by a combustion turbine, when using a liquidfuel, including means to inject a combustion catalyst suitable forreducing the quantity of particles generated by the installation.

This system also includes the means of measurement of the quantity ofparticles emitted and a central control unit suitable for controllingthe injection means so as to inject the combustion catalyst into thecombustion turbine when the measured quantity of particles is higherthan a maximum threshold value and to stop the injection of the catalystwhen the measured quantity of particles reaches a minimum target value.

The invention also concerns a gas turbine installation comprising asystem of control as defined above.

Other objectives, characteristics and advantages of the invention areprovided in the following description, given only by way of non-limitingexample, and with reference to the drawings attached, in which:

FIG. 1 is a synoptic diagram of the constitution of an installation ofgas turbine comprising a system of control according to the invention;and

FIG. 2 shows the curves illustrating the successive phases of injectionof fuel and stopping of the injection.

First of all, please refer to FIG. 1 which illustrates the structure ofa combustion turbine system according to an embodiment of the invention.

As it can be seen, the combustion turbine, designated by the generalreference number 1, successively includes a compressor 2 which ensuresthe compression of the ambient air admitted at the inlet of thecombustion turbine, one or more combustion chambers 3 in which thecompressed air from the compressor is mixed with a fuel and ignited, anda turboexpander 4 in which the ignited gas is expanded to producemechanical energy for driving the compressor and to provide themechanical energy required for the application implementing thecombustion turbine.

At the outlet, gas is recovered by an exhaust system 5 connected to anenergy recovery boiler 6 for evacuation to the outside through a chimney7.

The combustion chambers 3 are fed with fuel, in this case a liquid fuel,through an inlet line 8 connected to a fuel source 9 and equipped with aflow regulator 10.

As indicated earlier, the combustion in the combustion chambers 3produce the solid particles, such as soot. These particles pass throughthe turboexpander 4, the exhaust system 5, the boiler 6, and are emittedto the outside by the chimney 7.

The combustion turbine system 1 includes injection means 10 to inject acombustion catalyst into the gas turbine in order to reduce the quantityof solid particles, and more particularly the concentration of solidsgenerated during combustion.

The injection means 10 can be directly connected to the combustionchambers 3 so as to inject the combustion catalyst into the combustionchambers.

They can be also connected, as represented, to liquid fuel feed line 8so as to inject the combustion catalyst into the feed line 8.

The injection means 10 comprise a central control unit 11, a device 12for measurement of the concentration of particles emitted at the outletof chimney 12 and a measurement device 13 for measuring the liquid fuelflow in the feed line 8.

The central control unit 11 comprises a first controlling stage 14 whichincludes a mapping 15 in which the reference flow values of combustioncatalyst Qrefcat are stored as a function of reference flow values offuel Qrefcomb. From the flow value of fuel QF delivered by themeasurement device 13, the first controlling stage 14 retrieves acommand catalyst flow value Ccat from the mapping 15.

In other words, it concerns adapting the combustion catalyst injectionflow as a function of liquid fuel flow, which itself depends on thecharge level of the element driven by the combustion turbine, forexample an alternator.

The central control unit 11 also comprises a second controlling stage 16which receives the soot flow value Qsuies provided by the measurementdevice 12. These measured values are compared using comparators 17 and18 with a maximum threshold value and a minimum target value.

The output of the comparators 17 and 18 is provided to a combined logiccircuit, constituted, for example, by a RF rocker whose output dependson the value of the concentration of soot with respect to the thresholdvalue.

The output of the RF rocker switches to a high level, if the sootconcentration Qsuies is higher than the maximum threshold value andswitches to a low level, if the soot concentration reaches a minimumtarget value, and maintains its status, if the soot concentration isbetween minimum target value and the maximum threshold value.

The combustion catalyst injection means 10 comprise two redundantcatalyst injection lines L1 and L2, where one is an injection lineintended to be used during normal operation of the installation and theother one is an optional emergency injection line. The injection lineseach are controlled by command signals Cde1 and Cde2 coming from thecombined logic circuit 7 through a first component 19, a switch type, tocontrol the operation or shutdown of the two injection lines L1 and L2and two components 20 and 21, also switch type, to selectively controlthe operation of the injection lines L1 and L2.

Each of the injection lines L1 and L2 comprises a dosing pump,respectively P1 and P2, fed from a combustion catalyst feed system 22and driven by an electric motor M, which itself is powered byalternative sources, such as 23, through converters 24 receiving thecommand catalyst flow signal Ccat and driven by the command signals Cde1and Cde2. The output of each of the dosing pumps P1 and P2 is connectedto liquid fuel feed line 8 through valves such as 25.

So, when the central control unit 11 detects that the soot concentrationmeasured by the measurement device 12 is higher than the maximumthreshold value, it commands the dosing pump by keeping the commandsignal Cde 1 at the high level in order to power the motor M so as todeliver a combustion catalyst flow Ccat retrieved from the mapping 15 asa function of a fuel flow and a reference catalyst flow.

If the concentration of solid particles becomes lower than the minimumtarget value, then the injection of combustion catalyst is stopped.

For example, for a combustion turbine generating a rated electricalpower of 100 MW and consuming about 32 tonnes/hour of liquid fuel, theratio between the combustion catalyst flow and the liquid fuel flow ispreferably between 0.003% and 0.006%, which represents between 1 and 2kg/hour of combustion catalyst. The central control unit 11 controls thedosing pump according to the measured concentration level of sootparticles.

Above the maximum concentration threshold value, for example between 45mg/Nm³ and 55 mg/Nm³, the central control unit 11 starts the dosingpump. Below the target value, for example between 20 mg/Nm³ and 30mg/Nm³, the central control unit 11 stops the dosing pump.

Preferably, the maximum threshold and target values will be set at 50mg/Nm³ and 25 mg/Nm³, respectively. Continuous monitoring of theconcentration level enables to restart the dosing pump later.

As indicated earlier, in case of failure of the first injection L1 line,the second injection L2 line is activated to ensure catalyst injectionbased on the signals Cde2 and Ccat.

Now please refer to FIG. 2, which illustrates the operation of thesystem of control described.

This figure illustrates the variation of concentration of particles as afunction of time (curve A) and shows the evolution depending on the timeof thickness D1, . . . , Dn, Dn+1 of a layer of catalyst deposited onthe inner wall of the turbine.

As it can be seen in FIG. 2, the phases of injection of combustioncatalyst are thus implemented in a cyclic manner during the operation ofthe combustion turbine.

The interval between two cycles of combustion catalyst injection isbased on the configuration of the installation. The duration between twocycles of consecutive injection (T1, T2, T3, Tn−1, Tn, Tn+1, etc.)increases depending on the time of use of installation. However, Tncorresponds to the maximum duration between two cycles of combustioncatalyst injection. Tn+1 is lower than or equal to Tn.

However, it should be noted that the injected active combustion catalystparticles adhere to the walls of the installation forming layers ofactive agents of variable thickness as a function of time, producing acatalytic effect of conversion of the solid particles into CO₂.

After the combustion catalyst injection is interrupted, the activeparticles adhering to the walls continue their catalytic conversioneffect. When catalyst injection is interrupted, the layers of activeparticles subjected to movement and/or propagation of combustion gasestend to be gradually carried away toward the chimney and simultaneouslyconsumed. As a result, the consumption of active particles is such thatthe catalytic effect disappears when all the active particles have beenconsumed. It is at this time that it is necessary to proceed to a newinjection of the combustion catalyst.

As this is being done, this effect allows to carry out combustioncatalyst injection sequences at intervals, whose duration decreases withtime, while the injection stopping sequences increase inverselyproportionately, up to a limit corresponding to the saturation of activeparticles on the walls of the installation. This saturation phenomenonis related to the thickness of the layers of deposits and the speed ofpropagation of the combustion gases. In other words, the layer of activeparticles does not thicken indefinitely, since the deposits aredestabilized and tend to fall off from the walls under the effect ofspeed of the combustion gas. The combustion catalyst injection intervaldepends on the result of measurement of the particle concentration,higher than 25 mg/Nm³ and lower than 50 mg/Nm³. The duration of theintervals depends on the inner surface of the walls of the combustioninstallation, the exhaust gas flow and the temperature.

The fuel used for feeding the combustion chambers can have varioustypes. For example, we can use a heavy fuel oil, crude oil, a heavy orlight distilled, gas oil, kerosene, naphtha, biodiesel, bioethanol.However, it should be noted that using other liquid fuel types is notbeyond the scope of the invention.

We can use cerium(III) oxide, cerium(IV) oxide or an iron oxide or amixture of these catalysts as the oxidation catalyst. The chemicalreactions of conversion of soot into carbon dioxide are as below:

For cerium(IV) oxide, the reaction is as below:

4CeO₂+C (suies)→2Ce₂O₃+CO₂.

For cerium (III), the reaction is as below:

Ce₂O₃+½O₂→2 CeO₂, and

4CeO₂+C (suies)→2 Ce₂O₃+CO₂.

It should be noted that cerium(III) is converted into cerium(IV) due tothe presence of oxygen in the flames:

Ce₂O₃+½O₂→2CeO₂

1. A method of controlling the quantity of solid particles emitted by acombustion turbine (1), during the combustion of a liquid fuel, byinjecting a combustion catalyst suitable for reducing the quantity ofsolid particles generated during combustion, characterized in, that itcomprises the following steps: Measuring the quantity of particles(Qsuies) emitted during combustion; Injecting the combustion catalystinto the combustion turbine when the concentration of particles measuredis higher than a maximum threshold value; and Stopping the injection ofthe catalyst when the measured quantity of particles is lower than aminimum target value.
 2. The method according to the claim 1, in whichthe temperature of the flame of the combustion turbine is more than orequal to 1363K.
 3. The method according to one of the claims 1 and 2, inwhich the catalyst is injected into a feed line (8) of the said liquidfuel system, upstream of the combustion system of the combustionturbine.
 4. The method according to one of the claims 1 and 2, in whichthe catalyst is injected into the combustion chambers (3) of acombustion system of the combustion turbine.
 5. The method according toone of the claims 1 to 4, in which the maximum threshold value is aparticle concentration range between 45 mg/Nm³ and 55 mg/Nm³.
 6. Themethod according to one of the claims 1 to 5, in which the minimumtarget value is a particle concentration range between 20 mg/Nm³ and 30mg/Nm³.
 7. The method according to one of the claims 1 to 6, in whichthe combustion catalyst includes at least an element selected from iron(III) oxides, cerium (III) oxides, cerium (IV) oxides and theirmixtures.
 8. The method according to one of the claims 1 to 7, in whichthe concentration of particles emitted is measured continuously.
 9. Asystem for controlling the quantity of solid particles emitted by acombustion turbine (1), during the combustion of a solid fuel,comprising combustion catalyst injection means (10) suitable forreducing the quantity of particles generated during the combustion,characterized in, that it comprises measurement means (12) for measuringthe quantity of emitted particles and a central control unit (11)suitable for activating the measurement means so as to inject thecombustion catalyst into the combustion turbine (1) when the measuredquantity of particles is higher than a maximum threshold value and tostop the injection of the catalyst when the measured quantity ofparticles is lower than a minimum target value.
 10. The installation ofturbine gas type, characterized in, that it comprises a system ofcontrol according to claim 9.